Optical image stabilization is typically provided in cameras and in other optical apparatuses, such as binoculars. Optical image stabilization is performed by providing a movable optical element within the optical system, which is moved to compensate for movement, such as from a hand tremor. As shown in FIG. 1, this is normally performed by an open loop system in which motion is detected by a gyro. The gyro signal is processed to remove gyro offset and then perform high pass filtering and integration. The resulting signal is used to control movement of the movable optical element.
Such open loop control may be subject to a number of errors. The offset and the sensitivity of the gyro both may vary with temperature. The motion compensator response also may vary with temperature. The integration in the signal processing may accentuate the problem.
In sophisticated cameras, these problems can be minimized by careful attention to the design and quality of electronic and mechanical components. However, in low-cost cameras, there may be a limit to the quality and consistency that can be achieved. Moreover, in applications such as cameras for incorporation in mobile phones, the physical size of the camera is limited, typically in the region of 1 cm3, and this very small size may necessitate compromises in opto-mechanical component performance.
Another known form of image stabilization is digital image stabilization, which is used in some video (moving picture) cameras. This is achieved by a combination of cropping and object tracking. Referring to FIG. 2, the output image 10 is cropped from a larger image area 12. Motion of an object 14 is tracked between frames. In FIG. 2, the object 14 moves by motion vectors x, y between frames. By moving the crop 10 by x, y, the object appears to remain stationary within the output video. The motion vector signals are typically filtered at 0.3 Hz to allow deliberate camera motion while removing any high frequency motion.